In the 3rd generation mobile communication system, traditional macro evolved NodeBs (eNodeBs) have been replaced by distributed eNodeBs. The distributed eNodeBs are featured by separation between baseband and radio, and adopt optical fibre or cable to implement the remote function; while the baseband and radio unit of the traditional eNodeBs are integrated. Baseband Units (BBUs) of the distributed eNodeB form a shared baseband pool. The baseband and the radio frequency parts are connected by a remote transmission means, for example, the optical fibre and cable. Remote Radio Units (RRUs) are placed at any place needed. The two independent parts of the distributed eNodeB are separated from each other and are developed separately.
The BBU and the RRU are connected by the optical fibre, and an interface between them has been stipulated by standards. The current mainstream interface standards include the Common Public Radio Interface (CPRI) and the Interface between the RRU and the BBU (IR). The CPRI is used more widely, and can support the transmission under single-mode and mixed-mode of multiple modes, such as the Global System for Mobile Communication (GSM), the Universal Mobile Telecommunications System (UMTS), the Code Division Multiple Access (CDMA) and the Long-Term Evolution (LTE).
The CPRI protocol bears three types of data: orthogonal IQ data, control word and signalling, wherein the transmission formats of the control word and signalling are relatively fixed, but the transmission of the IQ data is very flexible. The CPRI protocol merely specifies that the transmission of the IQ data needs to meet the rate (3.84 Mbps) of a basic frame of the CPRI transmission, so the IQ placing formats in the
CPRI frame format of different modes are different, and the IQ placing formats in the CPRI frame format of the mixed modes of different modes are different too, which causes the difference between realizations of framing and deframing of the IQ data.
As regards framing and deframing of the IQ data, most of the current implementation solutions are seeking for a relatively appropriate IQ data placing format in a basic frame of CPRI transmission, then conducting data framing and deframing processing according to features of this placing format, and the course of processing is implemented by using hardware.
However, the implementation of the above solution is high in hardware complexity; at the same time, with the development of CPRI protocol and the upgrade of system, the flexibility of this solution is limited. After the transmission bandwidth of different modes (single mode or mixed mode) changes, the IQ data placing format in a basic frame of the CPRI transmission will be influenced directly, which will lead to change of realizing way of hardware. So, how to adapt to the development of protocol and system better, and adapt to various possible IQ data placing formats becomes a key technology, and is also the main problem of improving the product vitality and the market competitiveness.